1. Field of the Invention
The present invention relates to a train communication system suitable for information communication in trains.
2. Description of the Related Art
In recent years, needs have grown for the passenger information services using a liquid crystal display and the like in trains, and technologies for delivering various service contents from a server installed in a train to display units and the like in each of the cars have become widely available.
In the conventional technology described in Japanese Patent Laid-Open Publication No. 2002-209193, a train information device that processes train information such as train operation information including stop station information, arrival time, and the like, train location information indicating kilometers from the starting station, and train-mounted apparatus information including door open-close instruction and the like is installed in each of the cars. The train information device of the lead car is connected to various control operation devices such as a master control unit, and the train information devices installed in the cars are connected to each other through a digital transmission path, working in concert with each other to input and output the various train information.
An image information delivery device installed in the lead car is connected to the train information device in the same car, and receives train information and outputs still image information. The still image information is outputted as digital data signals through a first transmission path connecting the train information devices, then goes through the train information device installed in each of the cars, and is transmitted to a receiver/display device installed in each of the cars. The image information delivery device is connected to the receiver/display device installed in each of the cars through a second transmission path connecting the image information delivery devices and transmits moving image information as analog data signals.
As for the still image information having a smaller data size compared to the moving picture information, high-resolution still image information is digitally transmitted by a packet system which has been conventionally used in the train information device. On the other hand, the moving picture information having a larger data size than the still image information is transmitted by an analog transmission system such as an NTSC system which has been conventionally used in a television set and the like, enabling a train-mounted image delivery display system that realizes moving images and high-quality still images at low cost. In addition, because a system is employed that transmits the moving image information and the still image information to the receiver/display device via different paths, even if abnormality occurs in either one of the transmission paths, image information by moving images or still-images can be continuously displayed using the normal transmission path, so that the reliability of the display function is improved.
However, in the conventional technology described in Japanese Patent Laid-Open Publication No. 2002-209193, when transmitting the moving picture information as analog data signals, a considerably wide communication frequency band is required to transmit high-quality images. Because a plurality of cars are connected in a train, signal degradation occurs even if, for example, the analog signals are amplified and relayed using an amplifier or the like. In addition, because electro-magnetic noise generated by an inverter or the like installed in a train is superimposed on the analog signals, delivery of high-quality images to each of the cars is difficult.
When delivering images by analog data signals, multi-channel communication in which a plurality of pieces of moving image information or audio lines of a telephone and the like are multiplexed is provided in one transmission path, so that further wider frequency band is required which is difficult to realize. In addition, disconnection of a transmission line between cars or failure of a communication device in a train prevents transmission of the moving image information or the still image information to the display unit such that the information cannot be displayed.
An object of the present invention is to easily realize transmission of high-quality moving image information and audio information by digital data signals, and to reduce the influence of disconnection of a transmission line or failure of a communication device, thereby providing a highly reliable communication system in trains.